1. Field of the Invention
The present invention relates to an ultrasonic motor having a vibratory body and, more particularly, to an ultrasonic motor having a vibratory body in which the configuration of grooves formed in the vibratory body and a method of forming the grooves in the vibratory body have been improved.
2. Description of the Related Art
Ultrasonic motors have been disclosed, for example, in JP-B-1-40597 (Japanese Examined Patent Publication 1-40597). This kind of ultrasonic motor has a pressure welded vibratory body and a moving body. A piezoelectric body, for instance, which generates vibrations, is mounted in the vibratory body, and by being excited, gives rise to traveling vibratory waves. The moving body is frictionally driven by means of these vibratory waves.
This kind of ultrasonic motor results in achieving high torque even when operating at low speed, and is put to practical use in various mechanisms of cameras, etc.
FIG. 9 is a plan view showing one example of the vibratory body of a prior art ultrasonic motor. As shown in FIG. 9, the vibratory body 10 has an approximately annular shape, and plural grooves 11 are formed in its surface along the circumferential direction. These grooves 11 are formed in order to increase the amplitude of the vibration of the vibratory body 10. The grooves 11 are directed approximately perpendicular to the direction of advance (circumferential direction) of the vibratory waves, or in other words, are formed so as to be directed in radial directions of the vibratory body 10. Namely, as shown in FIG. 9, the grooves 11 are formed parallel with respect to lines I--I, II--II extending in the radial direction and passing through the axis (central portion) of the vibratory body 10.
The grooves 11 of the vibratory body 10 are formed one at a time by a groove forming member comprising a grindstone, etc., which revolves in order to successively cut into the surface of the vibratory body 10. Approximately 100 grooves are generally formed in the vibratory body 10.
However, in the above ultrasonic motor, when vibrational waves are generated in the vibratory body 10, resonance of the grooves may occur. As a result of this resonance, anomalous sounds are generated during the driving of the ultrasonic motor.
In addition, in the prior art method of preparing the vibratory body of the ultrasonic motor, as described above, an excessive amount of time is required to prepare the grooves of the vibratory body 10 because the grooves 11 are formed one by one, resulting in a high manufacturing cost.